The use of special carbon fibers referred to as carbon nanomaterials as reinforcing materials has received a great deal of attention in recent years, and various activation methods have been offered. Carbon nanofiber (CNF) which is a typical example of a carbon nanomaterial is a material in which a sheet of carbon atoms arranged in a hexahedral lattice is wound in the form of a tube. The material is referred to as a carbon nanofiber (or carbon nanotube) because the diameter is 1.0 to 150 nm (nanometers). The length is from a few micrometers to 100 μm.
When matrix metal stock is reinforced with carbon nanomaterial, it is necessary for the carbon nanomaterial to be dispersed uniformly in the matrix metal stock. This type of dispersion technique is known, for example, in Japanese Patent Application Laid-Open Publication No. 2006-265686 (JP 2006-265686 A).
A method for producing a nickel (Ni)/carbon nanotube (CNT) composite sintered body using the dispersion technology disclosed in JP 2006-265686 A referred to above is described in reference to the flow chart shown in FIG. 13 hereof.
In step (“ST” below) 101, the carbon nanotubes (CNTs), dispersant (sodium dodecyl sulfate), and solvent (purified water) are prepared, and the materials are combined and stirred/mixed for 1 h using ultrasound (ST102). In addition, in ST103, nickel (Ni) powder, dispersant (ammonium polyacrylate), binder (polyvinyl alcohol), and solvent (purified water) are prepared, the materials are combined, and stirring/mixing is carried out for 1 h using ultrasound (ST104).
The CNT suspension obtained in ST102 and the Ni slurry obtained in ST104 are combined, stirred/mixed by ultrasonication (ST105), and then heated to 80° C. and aggregated (ST106) to obtain an Ni/CT mixed slurry (ST107).
Next, the Ni/CNT mixed slurry is dried in two stages and compressed (ST108) to obtain a green molded body (ST109).
The resulting green molded body is defatted for 30 h (ST110) and then a sintering treatment is carried out under compression in a vacuum (ST111). An Ni/CNT composite sintered body is thereby obtained (ST112). With this technology, a favorable CNT dispersion will be produced based on inspection of the resulting Ni/CNT composite sintered body using a microscope.
The following conclusions regarding the above conventional technique were confirmed by the inventors of the present invention.
Firstly, production costs are high due to the necessity of a defatting treatment step (ST110) that lasts as long as 30 h.
Secondly, although dispersibility is favorable, the increase in strength is not as great as expected.
Specifically, the conventional technology has room for improvement in regard to production costs and strength increase.